Progressive add lenses (PALs) are used to provide vision correction for near vision issues, such as presbyopia. Progressive add lenses are designed to have distance, near, and intermediate viewing zones. The intermediate zone joins the near and distance zones in a cosmetically acceptable way, such that no discontinuities in the lens are visible to people observing the wearer. PALs also provide the wearer with vision correction at multiple distances without the need for multiple breaks in the lens or multiple pairs of glasses.
However, in a significant percent of PAL wearers, the optical (pupillary) axis measurement commonly used by the optical industry produces an incorrect segment separation because the optical (pupillary) axis of the eye is not always the same as the visual axis of the eye. This biometric issue is called angle Kappa. The visual axis is one's line of vision, which is a straight line that joins the fovea of the eye with a fixation point. A consequence of using the optical (pupillary) axis measurement only for determining the placement of PAL viewing zones within eyeglass lenses is that the placement of the PAL viewing zones while aligning with the optical (pupillary) axes may not properly align with the patient's visual axes and, thus, the patient may experience blurriness and various forms of visual and physical discomfort, due to the subject's degraded binocular vision. In particular, the viewing areas of progressive lenses are narrow and, thus, any slight misalignment is disruptive to binocular vision. As a result, the patient is dissatisfied with his/her PAL eyeglasses and further time and money is spent for return visits to the eye care provider for follow-up corrective action. For these reasons, a need exists for new approaches for determining and/or verifying the accurate placement of PALs in a subject's eyeglass frames.
There are many negative factors with a PAL prescription that can cause a patient to experience visual or physical discomfort. These issues can include wrong segment height, PAL style, frame fitting issues, an incorrect prescription, and/or horizontal misalignment. These negative factors need to be discovered and corrected for the PAL wearer to have glasses that function correctly and comfortably. The optical industry has equipment and techniques for determining, verifying and correcting all these factors in a PAL prescription, except there is currently no apparatus or method for validating and correcting the horizontal visual axes alignment. Thus there is a need in the art for an apparatus and method that fills this void in the validation and correction process of this alignment issue.